The present invention relates generally to noise cancellation, and more particularly, to a method and apparatus for reducing background noise during a telephone call.
Telephone service is currently available in just about every environment. Telephone calls can be made from mobile or stationary telephones located in a variety of environments including: city street corners, athletic stadiums, and inside an automobile. The environment from which a telephone call is made can hinder the ability of the caller to effectively communicate with the called party. As the background noise level in the environment from which the call is made approaches or exceeds the voice level of one or both parties to a telephone call, one party may not be able to hear the other party""s voice.
Some practical solutions applied by telephone customers when background noise levels are interfering with the customer""s ability to hear voices over the telephone include: physically moving to an alternate location with lower background noise levels before placing the call and if possible, waiting for the background noise to subside before placing the call. However, there are circumstances when one or more of the above solutions are ineffective or impractical. For example, the nearest alternate pay telephone may be a great distance away from the customer""s current location or the noise levels at a construction site may not subside until after construction work ceases at the end of the day.
One technique for reducing background noise during a telephone call is with a headset comprising both a microphone connected to a rotating boom and a speaker. The headset speaker is positioned over the user""s ear and the rotating boom is positioned so the microphone is near the user""s mouth. As the user speaks into the microphone during a telephone conversation, the microphone filters out background noise. However, such headsets are intended for use in conjunction with a home or office telephone. This product is not practical for use by someone using a pay telephone near a noisy construction site or near a busy street corner.
Another system which shifts the burden of reducing background noise levels from the telephone customer to the telephone system was developed by ATandT. This system makes a real-time measurement of the background noise level during a call, generates a signal representing the inverse of the measured background noise waveform, and transmits the inverse noise waveform over the telephone line during the telephone call to cancel the measured background noise level. However, this system measures the background noise level after the call is completed. Thus, after completion of the call, there are a few seconds during which background noise levels can interfere with the customer""s ability to hear voices over the telephone.
In view of the above, it can be appreciated that there is a need for a system which solves the above described problems by filtering background noise from a telephone call.
One embodiment of the present invention reduces background noise during a telephone call. After a caller initiates a call by dialing a telephone number, the system receives an ambient background noise level measured at the caller""s location. The system then computes an inverse noise waveform, which corresponds to the measured noise level, and transmits the inverted noise waveform along the line, which will be used by the completed telephone call. When the ambient background noise level from the caller""s location and the computed inverse noise waveform are transmitted along the same line during the completed call, the background noise level from the caller""s location is reduced.